July 23 (Reuters) - Wall Street's main indexes opened lower on Thursday, as concerns resurfaced about massive spending on artificial intelligence following the first batch of results from major technology companies, while another rise in oil prices due to escalating conflict in the Middle East further dampened investor sentiment.

The Dow Jones Industrial Average fell 463.0 points, or 0.89 percent, to 51,755.54 at the open. The S&P 500 declined 80.7 points, or 1.08 percent, to 7,418.29, and the Nasdaq Composite lost 445.4 points, or 1.73 percent, to 25,245.542.